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Mayo Clinic Health Library

E. coli

Updated: 10-10-2020

Overview

Escherichia coli (E. coli) bacteria normally live in the intestines of healthy people and animals. Most types of E. coli are harmless or cause relatively brief diarrhea. But a few strains, such as E. coli O157:H7, can cause severe stomach cramps, bloody diarrhea and vomiting.

You may be exposed to E. coli from contaminated water or food — especially raw vegetables and undercooked ground beef. Healthy adults usually recover from infection with E. coli O157:H7 within a week. Young children and older adults have a greater risk of developing a life-threatening form of kidney failure.

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Symptoms

Signs and symptoms of E. coli O157:H7 infection usually begin three or four days after exposure to the bacteria. But you may become ill as soon as one day after exposure to more than a week later. Signs and symptoms include:

  • Diarrhea, which may range from mild and watery to severe and bloody
  • Stomach cramping, pain or tenderness
  • Nausea and vomiting, in some people
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Causes

Only a few strains of E. coli trigger diarrhea. The E. coli O157:H7 strain belongs to a group of E. coli that produces a powerful toxin that damages the lining of the small intestine. This can cause bloody diarrhea. You develop an E. coli infection when you ingest this strain of bacteria.

Unlike many other disease-causing bacteria, E. coli can cause an infection even if you ingest only small amounts. Because of this, you can be sickened by E. coli from eating a slightly undercooked hamburger or from swallowing a mouthful of contaminated pool water.

Potential sources of exposure include contaminated food or water and person-to-person contact.

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Risk factors

E. coli can affect anyone who is exposed to the bacteria. But some people are more likely to develop problems than are others. Risk factors include:

  • Age. Young children and older adults are at higher risk of experiencing illness caused by E. coli and more-serious complications from the infection.
  • Weakened immune systems. People who have weakened immune systems — from AIDS or from drugs to treat cancer or prevent the rejection of organ transplants — are more likely to become ill from ingesting E. coli.
  • Eating certain types of food. Riskier foods include undercooked hamburger; unpasteurized milk, apple juice or cider; and soft cheeses made from raw milk.
  • Time of year. Though it's not clear why, the majority of E. coli infections in the U.S. occur from June through September.
  • Decreased stomach acid levels. Stomach acid offers some protection against E. coli. If you take medications to reduce stomach acid, such as esomeprazole (Nexium), pantoprazole (Protonix), lansoprazole (Prevacid) and omeprazole (Prilosec), you may increase your risk of an E. coli infection.
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Complications

Most healthy adults recover from E. coli illness within a week. Some people — particularly young children and older adults — may develop a life-threatening form of kidney failure called hemolytic uremic syndrome.

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Prevention

No vaccine or medication can protect you from E. coli-based illness, though researchers are investigating potential vaccines. To reduce your chance of being exposed to E. coli, avoid swallowing water from lakes or pools, wash your hands often, avoid risky foods, and watch out for cross-contamination.

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Diagnosis

To diagnose illness caused by E. coli infection, your doctor sends a sample of your stool to a laboratory to test for the presence of E. coli bacteria. The bacteria may be cultured to confirm the diagnosis and identify specific toxins, such as those produced by E. coli O157:H7.

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Treatment

For illness caused by E. coli, no current treatments can cure the infection, relieve symptoms or prevent complications. For most people, treatment includes:

  • Rest
  • Fluids to help prevent dehydration and fatigue

Avoid taking an anti-diarrheal medication — this slows your digestive system down, preventing your body from getting rid of the toxins. Antibiotics generally aren't recommended because they can increase the risk of serious complications and they don't appear to help treat the infection.

If you have a serious E. coli infection that has caused a life-threatening form of kidney failure (hemolytic uremic syndrome), you'll be hospitalized. Treatment includes IV fluids, blood transfusions and kidney dialysis.

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Lifestyle and home remedies

Follow these tips to prevent dehydration and reduce symptoms while you recover:

  • Drink clear liquids. Drink plenty of clear liquids, including water, clear sodas and broths, gelatin, and juices. Avoid apple and pear juices, caffeine, and alcohol.
  • Avoid certain foods. Dairy products, fatty foods, high-fiber foods or highly seasoned foods can make symptoms worse.
  • Eat meals. When you start feeling better, you can return to your normal diet.
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Preparing for an appointment

Most people don't seek medical attention for E. coli infections. If your symptoms are particularly severe, you may want to visit your primary care doctor or seek immediate care.

Here's some information to help you get ready for your appointment and know what to expect from your doctor.

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